Which gaming loyalty innovation first introduced the concept of 'Battle Pass' progression systems that later became industry standard across multiple gaming platforms?

In the competitive world of gaming, loyalty programs have evolved dramatically to keep players engaged. From basic point systems to complex multi-tier rewards ecosystems, gaming companies have pioneered innovative ways to build player retention. This trivia question explores a significant turning point in gaming loyalty program history that changed how developers approach player retention and community building.

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Dota 2's Compendium (2013)
World of Warcraft's Subscription Rewards (2010)
Call of Duty's Season Pass (2011)
League of Legends' Champion Mastery System (2015)